Gas barrier films in which a thin layer of a metal oxide such as aluminum oxide, magnesium oxide, or silicon oxide is formed on a plastic substrate or on a film surface, have been widely used in packaging of products which require a barrier for various types of gases such as water vapor and oxygen as well as in packaging to prevent changes in the quality of foods, industrial products, medicinal products and the like. Aside from the use for packaging, gas barrier films are also used as substrates for liquid crystal displays, solar cells, organic electroluminescence (EL) and the like.
An aluminum foil is widely used as the packaging material in these kinds of fields, but disposal after use is problematic and in addition, these are basically opaque materials and the fact that the content cannot be checked from the outside is also problematic. In addition, transparency is required for display materials, and these opaque materials cannot be used.
Meanwhile, a polyvinylidene chloride resin or copolymer resin materials of vinylidene chloride and another polymer or a material which is provided with gas barrier properties by coating these vinylidene chloride resins on polypropylene resins, polyester resins or polyamide resins are widely used as packaging materials in particular, but at the incineration step, chlorine based gases are generated and this is currently problematic in view of environment preservation. Furthermore, the gas barrier properties are not necessarily sufficient and so they cannot be used in fields where high barrier properties are required.
In particular, in transparent substrates which are used more and more in liquid crystal display elements and organic EL elements in particular, in addition to the requirement in recent years to be light weight and large in size, there are also high level requirements of long term reliability and a high degree of freedom with regards to configuration. In addition, film substrates such as transparent plastic are now being used instead of glass substrates which easily break, and are heavy and difficult in increasing screen size. For example, Japanese Patent Publication Open to Public Inspection (hereafter referred to as JP-A) H02-251429 and JP-A H06-124785 disclose an example in which a polymer film is used as the substrate for an organic electroluminescence element.
However, there has been a problem in that the gas barrier property of a film substrate such as a transparent plastic film is inferior to that of a glass substrate. For example, when such a substrate having an insufficient gas barrier property is used as a substrate of the organic electroluminescence element, water vapor and air may penetrate the substrate to degrade the organic layer, resulting in loss of light emitting properties or durability. In addition, when a polymer substrate is used as an electronic device substrate, oxygen may pass through the polymer substrate, penetrate and diffuse into the electronic device causing problems such as deterioration of the device or making it impossible to maintain the required degree of vacuum in the electronic device.
In order to solve this type of problem, a gas barrier film substrate in which a thin metal oxide layer is formed on a film substrate is known. Layers in which silicon oxide (Patent Document 1) or aluminum oxide (Patent Document 2) is deposited on the plastic film are also known as the gas barrier used in packaging material or liquid crystal element. In either case, currently the layers have water vapor barrier properties that do not exceed about 2 g/m2/day or oxygen transmission that does not exceed about 2 ml/m2/day. In recent years, due to the EL displays which require greater gas barrier properties, increasing size of liquid crystal displays and development of high definition displays, water vapor barrier of around 10−3 g/m2/day is required for the gas barrier properties of the film substrate.
A gas barrier film having a structure in which a high density ceramic layer and flexible polymer layer which softens impact from outside are alternately laminated a number of times, is proposed as a method for meeting these requirements of high water vapor barrier properties (see Patent Document 3, for example). However, because the composition of the ceramic layer and the polymer layer is generally different, adhesion at the respective adhesion interfaces deteriorate and cause product deterioration such as layer stripping. In particular, the occurrence of adhesion deterioration is outstanding under severe conditions such as high temperature and high humidity or exposure to ultraviolet radiation for an extended period, and thus early improvement is desired.
A gas barrier film having a gradient structure in which a high density ceramic portion and flexible polymer portion which softens impact from outside are gradually changed without forming an interface, is proposed for this problem (see Patent Document 3, for example). However, adhesion does not deteriorate though it has different natures because there in no interface, to the contrarily, relaxation performance against impact from outside is insufficient, and rupture vibration is not inhibited when the impact has large rate of time change and sometimes cracking is propagated, and thus early improvement is desired.    Patent Document 1 Examined Japanese Patent Publication No. 53-12953    Patent Document 2 JP-A S58-217344    Patent Document 3 U.S. Pat. No. 6,268,695    Patent Document 4 JP-A H10-249990